During the course of our studies on the mechanism of action of enzymes we have carried out a detailed study of the nature of the complexes formed between L-glutamate dehydrogenase and a variety of ligands, including substrates, coenzymes, products and modifiers. We have summarize our findings of the complicated multiple interactions of these ligands and their catalytic coenzymes in a connectivity scheme involving a pattern of six subsites located on the enzyme surface. We are now engaged in further studies to determine the relationship of these subsites to the actual chemical structure of the protein and to identify the detailed mechanism of the ligand interactions in the hope of shedding further light on the nature of biological cooperativity at the molecular level.